<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    
</head>
<body>
    
    <h3>this</h3>
    <button id="btn">click me</button>


    <script type="text/javascript">

      function A(){

      }
      A.prototype={
        n:1
      }

      const a=new A()

      console.log('a',a)
      console.log('a.n',a.n)
      console.log('a__proto__.n',a.__proto__.n)

      A.prototype={
        n:2,
        m:3
      }
      const b=new A()

      console.log('b',b)
      console.log('b.n',b.n)
      
      
    </script>
</body>
</html>